Heh! This reminds me of an anecdote... The mouth of the Columbia River (near Portland, OR), has some of the most treacherous waters in any shipping lane in the world. To try to cut down on shipwrecks, the coast guard put a "lightship" out just beyond these waters. IIRC, it depended on hefty anchors AND engines ("extra inches of Swimming, Only to Hold Position") to stay on station. It worked pretty well, too, until a huge storm broke the anchor chains... The engines weren't enough to keep it from running aground several miles away.
Will Rhodes